1. Field of the Invention
The present invention relates to a reel hub for a magnetic tape cassette. More particularly, it relates to a magnetic tape clamping device of a reel hub for clamping a magnetic tape or a leader tape.
2. Description of the Prior Art
The conventional reel hub for a magnetic tape cassette has a clamping device for holding the end of a magnetic tape or a leader tape around the reel hub. FIGS. 1 and 2 illustrate a conventional reel hub in which a clamping device (4) is provided in a portion of the periphery of the reel hub (1). The reel hub (1) has a central opening (2) provided with projections (3) for engaging with the projections of a driving shaft. The magnetic tape clamping device (4) has a concave portion (5) formed in the circumference of the reel hub (1) and a clamping piece (7). Recesses (6) are respectively formed in both side walls (the front and rear walls in view of the rotating direction) of the concave portion (5) into which a resilient clamping piece (7) having the right and left projections (8) is fitted.
FIG. 3 illustrates another conventional reel hub having a circular concave portion into which a clamping piece (10) having a circular cross section is fitted.
In either case, the end portion of the magnetic tape or the leader tape T is clamped between the concave portion (5) or (9) and the clamping piece (7) or (10).
In the conventional reel hub having the structure described above, when a large pulling force is applied to the magnetic tape T, the clamping piece as shown in FIGS. 1 and 2 is bent to possibly cause detachment of the tape. In fact, such a trouble has been sometimes reported. The reel hub shown in FIG. 3 requires a high dimensional accuracy. A reel hub poor in accuracy is useless and it is difficult to produce a highly accurate product. If the magnetic tape clamping device is too loose, the magnetic tape is easily released and the clamping device is too tight, the tape is easily cut during the clamping operation.
A magnetic tape clamping device in which the side walls of the concave portion of the reel hub is formed elastic and a clamping piece is fitted into the concave portion to clamp a tape by utilizing elasticity is proposed in Japanese Examined Publication No. 30929/1970. In the magnetic tape clamping device, however, the elastic wall of the concave portion causes a deformation in the direction away from the magnetic tape when the tape is strongly pulled. Thus the conventional clamping device could not provide a sufficient retaining function.